1. Field of the Invention
The invention relates generally to work vehicles such as agricultural planters. More particularly, it relates to a hydraulic control system for an agricultural planter that includes a series of master cylinders having slave cylinders operably connected therewith. Even more particularly, it relates to a hydraulic control system wherein the master and slave cylinders can be operated independently of one another such that the master cylinder can be operated to effect distinct field transport and road transport heights.
2. Discussion of the Related Art
Conventional planters typically include a series of evenly spaced row planter units connected to an implement frame or tool bar so as to be towed across a field. The row planter units are generally configured to plant particulate product (i.e., seed, herbicide, pesticide, fertilizer, etc.) in evenly spaced individual rows. The planter is usually towed by a propelling vehicle such as a tractor or other prime mover across the field. As the planter, reaches the end of a row, or requires transport from a field to another more remote location, it is often necessary to reconfigure the planter from a field planting configuration or position to a field transport (for movement between planting rows), or folded road transport position.
In many prior art systems, hydraulic lift systems are utilized to reconfigure the planter to and from the above noted positions. In such prior art systems, remote hydraulic valves provide hydraulic flows to locations on the tool bar to adjust the positioning of the same. The valves are controlled in an operator station in the cab of the vehicle, most commonly by manipulating a control device that provides a signal and indicates a desired flow rate to or from the hydraulic valve. The hydraulic valves are typically connected to a manifold or manifolds, most commonly located at the rear of the vehicle, to which hydraulic actuators are mounted. The hydraulic actuators include such things as hydraulic motors and cylinders. By manipulating the control device, the operator can vary the flow direction and the flow rate to the manifold, and hence to the hydraulic actuators located on the tool bar.
However, known hydraulic systems have drawbacks. Most notably, in most prior art systems, the maximum road transport height (height used herein means the clearance of the tool bar from the ground) and the field transport height is often the same. This is due to the fact that when an operator strokes a master cylinder controlling the height of the central wheels to the exclusion of the slave cylinder controlling the wing wheels, both cylinders typically bottom out thereby limiting the maximum raised height of the planter tool bar from the ground. The limited maximum height of the road transport position has proved problematic when the planter needs to be moved long distances over ditches and other uneven surfaces. Portions of the planter may not have adequate clearance to cross these uneven surfaces. Likewise, the height (clearance of the tool bar from the ground) of the field transport position in many of these systems is unnecessarily high. As the field transport position most commonly only requires turning between adjacent rows, it is unnecessary to raise the system to the same height required for road transport.
There have been some attempts at providing a planter that can fold into distinct field transport and road transport configurations. For example, one known system includes a front fold planter configured such that when the wing wheels are retracted, oil from the slave cylinders in communication with the wing wheels is moved through a solenoid valve and routed into a master cylinder thereby stroking the master cylinders to achieve a higher road transport height. This system, while somewhat satisfactory for its intended purpose, exhibits drawbacks as the routing system is overly complex and costly to manufacture.
Therefore, there is a need or desire for a hydraulic control system for a work vehicle such as a front fold planter to address the drawbacks described above. The hydraulic control system should also be configured to be utilized with a wide variety of bar supported implements frames and/or vehicles in addition to those related to agriculture. The hydraulic control system should also be versatile so as extend its lifetime and minimize replacement. Also, the hydraulic system should be simple in design so as to reduce costs associated with labor and manufacturing.